BY LINDA McGURK
Indiana Correspondent WEST LAFAYETTE, Ind. — Weeds can decrease yields in minimal-tillage organic cropping systems, but contrary to popular belief, the soil quality can be superior to that in a conventional no-till system.
Those were the conclusions of two studies conducted over 12 years by USDA’s Agricultural Research Service (ARS) in Batesville, Md.
“What surprised me was that by adding cover crops and manure, we were able to increase the carbon and nitrogen, despite the fact that we did some tilling,” said John Teasdale, an ARS plant physiologist and the lead scientist for the studies.
While many studies have focused on soil quality in organic systems versus conventional plow-tillage systems, only a few have compared the organic matter in organic crop production with that in no-till systems. No-till systems are often thought to have a higher rate of soil organic matter, since traditional organic production is usually tillage-intensive in order to incorporate manure and control weeds.
Teasdale instead chose a minimal-tillage approach for the organic plots in the study, using a chisel plow and trying to keep the soil protected with cover crops while also adding manure. The performance of corn, soybeans and wheat on this plot was then compared with the same crops on standard no-till plots, no-till cover-crop plots and crownvetch living mulch plots.
During the first study, which lasted from 1994-2002, weeds lowered corn and soybean – but not wheat – yields in the organic cropping systems below levels of the no-till systems.
“The organic production didn’t do as well as the conventional system because it was hard to control the weeds with minimal tillage,” Teasdale explained. “Organic production does better with a more diverse rotation that includes hay.”
The short, grain-based rotation that’s typical for conventional cropping systems doesn’t suit organic production, since it allows certain weeds to mature and add their seeds to the soil.
Teasdale followed up the first nine-year study by growing corn with conventional no-till methods on all four plots for three years.
When comparing yields, it turned out the plot with a history of organic farming methods out-yielded the no-till plots by 18 percent. This plot also had more carbon and nitrogen.
Tony J. Vyn, agronomy professor at Purdue University, said a no-till system may still have a higher soil organic content for any given soil, considering organic producers need to rely more on tillage for weed control.
“An organic system doesn’t automatically confer better soil quality,” he said.
“When it does, it’s usually due to increased incorporation of cover crops, livestock manure and diverse rotation.”
A conventional cash crop farmer who is considering a switch from a corn-soybean rotation and reliance on fertilizers and pesticides may find the study useful, but Vyn offered a word of caution.
“There’s nothing wrong with comparing the systems,” he said. “But when you do, you need to know that the difference is much less dependent on eliminating fertilizers and pesticides than it is on adding manure and cover crops.”
Teasdale echoed that opinion, saying he doesn’t see a problem with a “judicious” use of herbicides to optimize yields, since there’s no conclusive evidence that it harms soil quality. Nor did he recommend a one-size-fits-all solution to finding an ideal cropping system.
“In most cases, you can say that the yield potential is better in soils with higher organic matter,” he said. “But it depends on what your goals are. Right now, a lot of farmers want to take advantage of high corn prices and the idea of a more complex system with cover crops and manure may not seem as viable.”
Others may want to take advantage of the premium offered on organic crops, in which case Teasdale recommended using less erodible land. “On more erodible land, I recommend a hybrid system with no-till and herbicides to manage weeds.”
This farm news was published in the Aug. 1, 2007 issue of Farm World, serving Indiana, Ohio, Illinois, Kentucky, Michigan and Tennessee. |
